Glass sheet bending mold having wear resistant surface

ABSTRACT

An improved glass sheet bending mold (10) disclosed comprises a stainless steel base (12) for receiving the heated glass sheet to be bent. An electrically deposited metal carbide coating (16) is deposited on the stainless steel base (12). A boron nitride covering (18) covers the metal carbide coating (16) to provide a forming surface (14) that is harder than the base (12) and is wetted less by the heated glass sheet than is the base.

TECHNICAL FIELD

This invention relates to an improved glass sheet bending mold of thetype used for bending heat softened flat glass sheets.

BACKGROUND ART

Forming molds having generally curved glass bending surfaces for bendingflat glass sheets into useful shapes such as automobile windshields,side windows and rear windows are generally fixed mold or articulatedmold types. The fixed mold can be used in a horizontal position wheregravity supplies the force that causes heat softened glass on the curvedmold to sag to the extent that it comes in contact with and completelyconforms to the shape of the bending surface of the mold as the glasssurface slides along the curved surface of the mold. As the glass slidesdown the surface of the mold, the natural abrasion of the glass againstthe bending surface causes glass marking and mold wear. Fixed molds arealso generally used for press bending heated glass sheets. In pressbending, the heated glass sheets are placed between male and female moldmembers and a mechanical force is used to press form the glass betweenthe bending surfaces of the mold members.

Alternatively, the articulated type mold has a hinged curved bendingsurface. The articulated mold also uses gravity to supply the force tobend the flat glass. This type of mold has particular application in theformation of glass sheets such as automobile windshields where theradius of curvature near the edge of the glass sheet is less than thatof the windshield as a whole. Unlike the fixed shape glass forming mold,there is less tendency for the heat softened glass to slide along thesurface of the mold and cause marking of the glass sheet and relatedmold wear that is often created when a fixed mold is used with gravitysupplying the bending force. Articulated molds like fixed shape moldsare commercially used for forming flat glass sheets and the associatedproduction rates require a long mold life together with the ability toproduce a high quality glass product free from marks associated with hotglass sliding along the curved mold surface.

Conventional molds are normally made of iron, steel or ceramics. Some ofthese molds have been known to be coated with boron nitride, graphite orvarious fiberglass coverings. One such mold is known to have boronimpregnated directly into the surface of the mold. Nevertheless, livesof conventional molds are limited and often coatings on the molds mustbe continuously replaced. There is thus a need for a glass sheet bendingmold that has a long life while also minimizing glass marking even afterrepeated bending of the glass sheets.

Prior art references noted by a search conducted prior to filing thisapplication are discussed below.

U.S. Pat. No. 2,201,049 to R. W. Moore for Glass Fabrication Process andMold provides for mold members which are coated with boron nitride toprevent sticking of fluid glass to the solid mold surface.

U.S. Pat. No. 2,246,463 to Louis D. Garratt for Treatment of MoldSurfaces provides a process for depositing a graphite layer on thesurface of a forming mold.

U.S. Pat. No. 2,560,599 to J. D. Ryan for Bending Mold and Method ofProlonging the Life Thereof provides for a glass forming mold having afiberglass cover and filler.

U.S. Pat. No. 2,746,209 to E. L. Walters for Equipment for Bending GlassSheets calls for a cast iron mold having high percentages of nickel andchromium.

U.S. Pat. No. 3,295,346 to H. B. Bomberger, Jr. for Methods for theElevated Temperature Production of Metallic Surfaces, and CoatingsTherefor discloses a boron oxide and feldspar coating for a metalsurface exposed to hot processing.

U.S. Pat. No. 3,506,430 to W. W. Oelke et al for Glass Sheet BendingMold discloses a fiber metal material covering for bending molds.

U.S. Pat. No. 3,586,493 to G. R. Claassen for Mold for Bending GlassSheets provides for a refractory insulating coating on a bending mold.

U.S. Pat. No. 3,713,798 to Stilley et al for Method of Press ShapingGlass Sheets discloses a method of bending heat softened glass sheetsagainst a mold member that uses a fiberglass fabric cover.

U.S. Pat. No. 3,899,316 to Ehlers for Bending of Glass Sheets provides amethod of bending heated glass sheets against a resilient layer ofalumino silicate fibermat material covering a mold surface.

U.S. Pat. No. 3,973,943 to Seymour for Apparatus for Supporting ShapedGlass Sheets for Tempering discloses a forming mold having a fiberreinforced resin material covering.

U.S. Pat. No. 3,994,707 to Newing, Jr. et al for Solid Film LubricantLaminates and Their Use in Glass Manufacturing discloses a metal moldcovering of nickel and chromium and metal carbides and/or transitionmetal nitrides together with a graphite lubricant layer. One disclosedcomposition of the covering has 61% Ni and 7% Cr and about 12% by weightof tungsten carbide.

U.S. Pat. No. 4,382,811, to Luscher et al for Method of ProducingProtective Coating On Metal Parts to be Used in Contact With MoltenGlass presents a method of flame spraying the metal part with ,hromiumoxide and a nickel base alloy.

U.S. Pat. No. 4,251,254 to Klomp et al for Tools for the and Shaping ofGlass discloses a tool made oi a boron containing material for thehandling and shaping of glass at low viscosity.

U.S. Pat. No. 4,274,857 to Wolfe for Treating Covers for Press BendingMolds, and Method of Press Bending Glass Sheets provides a flexiblecover of fiberglass fabric impregnated with a dispersion of boronnitride to be used as a cover with a press bending mold.

DISCLOSURE OF INVENTION

An object of the present invention is to provide an improved flat glassforming mold having a curved bending surface that tends not to stick toheat softened glass sheets and thereby reduces glass marking associatedwith the glass sheets sliding along the bending surface during thebending process.

Another object of the present invention is to provide a hard flat glassforming mold having high temperature resistance necessary to repeatedlyengage hot glass and provide for an extended mold life.

In carrying out the above objects, the improved flat glass forming moldcomprises a curved base for receiving the glass sheet to be bent. Aglass engaging coating is applied on the base to provide a coating thatis harder than the base and is wetted less by the heated glass sheetthan is the base.

In a preferred construction, the mold has a fixed curvature. Also, thecurved base of the forming mold is preferably made of stainless steel.Furthermore, the glass engaging coating is preferably made of a metalcarbide composition, most preferably tungsten carbide.

In the preferred embodiment, the metal carbide coating is an electricaldeposit about 0.003 inches thick. Preferably, the coating is a plasmadeposit of the metal carbide composition although the metal carbide canbe an electrostatic deposit or the result of other processes.

The forming mold includes a covering of boron nitride over the metalcarbide coating. In the preferred practice disclosed, the boron nitridecovering is a paste of boron nitride powder and water spread over themetal carbide coating although other coating processes may also be used.

The above object and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the best mode for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a closed ring type flat glass formingmold constructed in accordance with the present invention; and

FIG. 2 is an enlarged view of a glass engaging surface of the formingmold.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 1 of the drawings, a glass forming mold accordingto the present invention is generally indicated by 10 and is used tobend heat softened flat glass sheets. As is more fully hereinafterdescribed, the flat glass forming mold 10 reduces glass marking and moldwear associated with the bending of hot glass sheets and is highlytemperature resistant. Although the forming mold 10 shown is a fixedshape closed ring mold type, the same invention can be used with anarticulated type glass forming mold and other flat glass forming moldseven though the invention has particular utility for molds of fixedshapes.

As shown in FIG. 1, the forming mold 10 comprises a fixedly curved base12 for receiving a glass sheet to be bent. Curved base 12 has a glassforming surface 14 on which glass sheets are placed. The mold 10 andglass sheet are passed through a furnace where the heating softens theglass such that the sheet sags toward the shape of the forming surface14.

As the heat softened glass sags, the glass sheet slides along the glassforming surface 14 until the glass comes in contact with and completelyconforms to the shape of the forming surface 14. The forming mold 10 andformed flat glass sheet are subsequently removed from the furnace,allowed to cool, and the mold is reused.

As illustrated in FIG. 2, the curved base 12 is of a stainless steelmaterial. A glass engaging coating 16 of a metal carbide compositiorthat is harder than the base 12 and is wetted less by the heated glasssheet than is the base is electrically deposited onto the base at theglass forming surface 14. Coating 16 imparts a hard wear resistantsurface on the stainless steel base 12 and reduces glass marking andmold wear because of the lubricity of the surface 14.

In the preferred embodiment, the metal carbide composition is tungstencarbide which exhibits superior wear resistance and resistance to hightemperatures associated with bending hot glass sheets. In the preferredembodiment, the metal carbide coating is 0.003 inches thick.

The glass engaging coating 16 is preferably formed by a plasmadeposition process where the coating flows onto the base 12. Anelectrostatic deposition process is also suitable. Other depositionprocesses can also be used.

With further reference to FIG. 2, the coating 16 includes a covering 18of boron nitride over the metal carbide deposit. Coating 16 is wettedless by the heated glass sheet reducing the natural abrasion of the hotglass sheet as it slides along the forming surface 14 during the bendingprocess.

The boron nitride covering 18 is conveniently applied as a paste ofboron nitride powder and water spread over the metal carbide coating 16although any suitable application process can be used.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

What is claimed is:
 1. A forming mold for bending heated, flat glasssheets, the forming mold comprising: a curved base for receiving theheated glass sheet to be bent; and a glass engaging coating on the base,wherein the coating is harder than the base and is wetted less by theheated glass sheet than is the base.
 2. A forming mold as in claim 1wherein the curved base is stainless steel.
 3. A forming mold as inclaim 2 wherein the glass engaging coating comprises a metal carbidecomposition.
 4. A forming mold as in claim 3 wherein the metal carbidecomposition is tungsten carbide.
 5. A forming mold as in claim 3 or 4wherein the metal carbide composition is an electrical deposit.
 6. Aforming mold as in claim 5 wherein the electrical deposit iselectrostatically deposited.
 7. A forming mold as in claim 5 wherein theelectrical deposit is a plasma deposit.
 8. A forming mold as in claim 3or 4 wherein the metal carbide coating is about 0.003 inches thick.
 9. Aforming mold as in claim 3 or 4 further including a covering of boronnitride over the metal carbide coating.
 10. A forming mold as in claim 9wherein the boron nitride covering is a paste of boron nitride powderand water spread over the metal carbide coating.
 11. A forming mold asin claim 9 wherein the mold has a fixed curvature on which the hot glasssheet readily slides about the boron nitride covering to conform to theshape of the mold.
 12. A forming mold for bending heated, flat glasssheets, the forming mold comprising: a stainless steel base forreceiving the heated glass sheet to be bent; an electrically depositedmetal carbide coating on the stainless steel base; and a boron nitridecovering over the metal carbide coating.
 13. A forming mold for bendingheated, flat glass sheets, the forming mold comprising: a stainlesssteel base having a fixed curvature for receiving the heated glass sheetto be bent; an electrically deposited tungsten carbide coating on thestainless steel base; and a boron nitride covering spread as a pasteover the tungsten carbide coating.